Pain is an unpleasant feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain's widely defined ‘pain’ as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage” (Pain 1979; 6:247-8). Pain is the most common reason for physician consultation in the United States (Raj P P. Taxonomy and classification of pain. In: Niv D, Kreitler S, Diego B, Lamberto A. The Handbook of Chronic Pain. Nova Biomedical Books 2007). It is a major symptom in many medical conditions, and can significantly interfere with a person's quality of life and general functioning (Breivik H, Borchgrevink P C, Allen S M, Rosseland L A, Romundstad L, Hals E K, Kvarstein G, Stubhaug A. Assessment of pain. Br J Anaesth. 2008; 101(1):17-24). In most cases, pain is usually transitory, lasting only until the noxious stimulus is removed or the underlying damage or pathology has healed. However, some painful conditions, such as rheumatoid arthritis, peripheral neuropathy, cancer and idiopathic pain, may persist for years. Pain that lasts a long time is called ‘chronic’, and pain that resolves quickly is called ‘acute’. Traditionally, the distinction between acute and chronic pain has relied upon an arbitrary interval of time from onset; the two most commonly used markers are 3 months and 6 months since the onset of pain (Turk D C, Okifuji A. Pain terms and taxonomies of pain. In: Bonica J J, Loeser J D, Chapman C R, Turk D C, Butler S H. Bonica's management of pain. Hagerstwon, Md.: Lippincott Williams & Wilkins; 2001), though some researchers have placed the transition from acute to chronic pain at 12 months (Spanswick C C, Main C J. Pain management: an interdisciplinary approach. Edinburgh: Churchill Livingstone 2000). Others apply ‘acute’ to pain that lasts less than 30 days, ‘chronic’ to pain of more than six months, and ‘subacute’ to pain that lasts from one to six months (Thienhaus O, Cole B E. Classification of pain. In: Weiner R. Pain management: a practical guide for clinicians. Boca Raton: CRC Press; 2002).
In humans, the detection of peripheral pain begins at free nerve endings. The polymodal pain receptors and high threshold mechanoreceptors detect noxious stimuli such as strong mechanical forces, H+, K+, chemicals, and temperature. After detection of the stimuli, the sensation of pain travels from the periphery to the spinal cord (i.e., the spinothalamic tract), then decussate and cross via the anterior white commissure (in the spinal cord) before ascending contralaterally. Before reaching the brain, the spinothalamic tract splits into the lateral neo-spinothalamic tract and the medial paleo-spinothalamic tract (Skevington, S. M. Psychology of pain. Chichester, UK: Wile 1995; p 18), subsequently terminating at the ventral posterolateral nucleus of the thalamus, where they synapse on dendrites of the somatosensory cortex. Apart from noxious stimuli causing pain, injuries to a peripheral nerve in humans often results in a persistent neuropathic pain condition that is characterized by spontaneous, usually burning pain, allodynia (pain responses to non-noxious stimuli) and hyperalgesia (exaggerated pain responses to noxious stimuli). Although sympatholytic therapy is sometimes effective for relief of the pain, indicating that neuropathic pain is at least partly maintained by activity in the sympathetic nervous system, many patients do not respond. The effectiveness of opioids for neuropathic pain is also limited (Rowbotham M C. Ann Neurol 1994; 35:S46-S49), and somewhat controversial.
Acute pain is usually managed with medications such as analgesics and anesthetics. Management of chronic pain or neuropathic pain, however, is much more difficult. Many drugs help relieving acute pain, and in general they can be divided into non-opiod and opiod drugs. The non-opiod drugs include non-steroid anti-inflammatory drugs (NSAIDs), such as acetylsalicylic acid (aspirin) and COX-2 (cyclooxygenase-2) inhibitors. The term “nonsteroidal” in NSAIDs is used to distinguish these drugs from steroids, which, among a broad range of other effects, have a similar eicosanoid-depressing, anti-inflammatory action. As analgesics, NSAIDs are unusual in that they are non-narcotic. NSAIDs are usually indicated for the treatment of acute or chronic conditions where pain and inflammation are present.
Aspirin is often used as an analgesic to relieve minor aches and pains, as an antipyretic to reduce fever, or as an anti-inflammatory medication. Aspirin works well for dull, throbbing pain, but it is ineffective for pain caused by most muscle cramps, bloating, visceral distension, and acute skin irritation. As a post-surgery painkiller, aspirin is inferior to one of the NSAIDs ibuprofen and has a higher gastrointestinal toxicity. Furthermore, aspirin also has many contraindications and undesirable effects; for example, the use of aspirin needs to be cautious in people with peptic ulcers, mild diabetes, or gastritis. Even if none of these conditions is present, there is still an increased risk of stomach bleeding. The other category of NSAIDs is COX-2 selective inhibitor that directly targets COX-2, an enzyme responsible for inflammation and pain. Targeting selectivity for COX-2 reduces the risk of peptic ulceration, and is the main feature of celecoxib, rofecoxib and other members of this drug category. COX-2 inhibitors also have adverse effects, most notably an increased risk of renal failure, and some results have shown an increase in the risk for heart attack, thrombosis and stroke by a relative increase in thromboxane. Of note, Rofecoxib (commonly known as Vioxx) was taken off the market in 2004 because of these concerns.
An alternative category of analgesics is opioid drugs. An opioid is a psychoactive chemical that works by binding to opioid receptors, which are found principally in the central and peripheral nervous system and the gastrointestinal tract. The receptors in these organ systems mediate both the beneficial effects and the side effects of opioids. The analgesic effects of opioids are due to decreased perception of pain, decreased reaction to pain as well as increased pain tolerance. Opioids have long been used to treat acute pain (such as post-operative pain), and are invaluable in palliative care to alleviate the severe, chronic, disabling pain of terminal conditions such as cancer, and degenerative conditions such as rheumatoid arthritis. However, opioids should be used very cautiously in chronic non-cancer pain. High doses are not necessarily required to control the pain of advanced or end-stage disease. Tolerance (a physical reaction making the body less responsive to analgesic and other effects) is very likely to occur, making the opioid as the last option for pain control.
From the discussion above, it is clear that there is an urgent need to develop a new class of effective non-tolerant and non-sedative analgesics for controlling both severe acute pain and chronic pain.
A mixture of bioactive agents extracted from skin tissue of rabbits with inflammation elicited by inoculation of the virus Vaccinia variolae, which contain inhibitors against the kallikrein-kinin system, has been used for treatment of pain for decades (K. Ono, A. Inoue, and M. Nakamuro. Jpn Pharmacol Ther, 1981; 9:299-307). Pharmacological and clinical experiments showed that such a mixture of bioactive agents prepared from the rabbit skin have analgesic effects against all kinds of symptomatic neuralgia, lumbago, cholecystagia, angina, arterial embolism pains, acute pains from wound, burn and scald, pains in surgery or post-surgery, peptic ulcer pain, dysmenorrhea, labor pains posterior to childbirth, headache, pains induced by various tumor and so on. Studies also showed that the this mixture of bioactive agents can effectively promote activation of macrophage, significantly inhibit the activity of anti-complement in type II allergic reaction. The effects have linear correlation with the doses. So the drugs have effects on inhibiting inflammatory reaction correlated with immunity and improving immunity function. Furthermore, after a continuous 28-day intraperitoneally administration of the drugs prepared from the rabbit skin in rats, no rats died and no changes induced by the drugs existed in examinations of urine, eye, blood biochemistry, pathology and anatomy. Therefore, such analgesic drugs have little toxic effects (See US Patent application number: 20110003009). However, although peptide research on drug design and drug discovery is one of the most promising fields in the development of the new drug, there was no report that the researchers in this field focus on searching the active protein ingredients in the mixture, even though such a mixture has been in the market for several decades and with good effects for analgesia. Therefore, identification of the active ingredient(s) will help understanding the acting mechanism(s), and purification of the exact components responsible for analgesic effects will facilitate the preparation of well-delineated drug(s) for clinical use.
Influenzavirus A is a genus of the Orthomyxoviridae family of viruses. Strains of all subtypes of influenza A virus have been isolated from wild birds, although disease is uncommon. Some isolates of influenza A virus cause severe disease both in domestic poultry and, rarely, in humans (“Avian influenza (“bird flu”)—Fact sheet”. WHO.) Occasionally, viruses are transmitted from wild aquatic birds to domestic poultry, and this may cause an outbreak or give rise to human influenza pandemics (Klenk, et al. (2008). “Avian Influenza: Molecular Mechanisms of Pathogenesis and Host Range”. Animal Viruses: Molecular Biology. Caister Academic Press & Kawaoka Y, ed. (2006). Influenza Virology: Current Topics. Caister Academic Press). Influenza A viruses are negative sense, single-stranded, segmented RNA viruses. There are several subtypes, labeled according to an H number (for the type of hemagglutinin) and an N number (for the type of neuraminidase). There are at least 16 different H antigens (H1 to H16) and nine different N antigens (N1 to N9). Different influenza viruses encode for different hemagglutinin and neuraminidase proteins; for example, the H5N1 virus designates an influenza A subtype that has a type 5 hemagglutinin (H) protein and a type 1 neuraminidase (N) protein. Furthermore, each virus subtype has mutated into a variety of strains with differing pathogenic profiles; some are pathogenic to one species but not others, and some are pathogenic to multiple species. Theoretically, 144 different combinations of these proteins are possible (“Influenza Viruses”. Centers for Disease Control and Prevention. Nov. 18, 2005). Some variants are identified and named according to the isolate they resemble, thus are presumed to share lineage (example: Fujian flu virus-like), according to their typical host (example: human flu virus), according to their subtype (example: H3N2), and according to their deadliness (example: LP, low pathogenic). So a flu from a virus similar to the isolate A/Fujian/411/2002(H3N2) is called Fujian flu, human flu, or H3N2 flu.
“Human influenza virus” usually refers to those subtypes that spread widely among humans. Amongst all strains, H1N1, H1N2, and H3N2 are the only known influenza A virus subtypes currently circulating among humans (CDC, USA: Key Facts About Avian Influenza (Bird Flu) and Avian Influenza A (H5N1) Virus). Treatments for influenza include a range of medications and therapies that are used in response to disease influenza. Treatments may either directly target the influenza virus itself; or instead they may just offer relief to symptoms of the disease, while the body's own immune system works to recover from infection (Montalto N J, Gum K D, Ashley J V (2000). “Updated treatment for influenza A and B”. Am Fam Physician 62 (11): 2467-76). The two main classes of antiviral drugs used against influenza viruses are neuraminidase inhibitors, such as zanamivir and oseltamivir, or inhibitors of the viral M2 protein, such as amantadine and rimantadine. These drugs can reduce the severity of symptoms if taken soon after infection and can also be taken to decrease the risk of infection. However, viral strains have emerged with drug resistance to both classes of drug. Like the development of bacterial antibiotic resistance, this can result from over-use of these drugs. For example, a recent study emphasized the urgent need for augmentation of oseltamivir (Tamiflu) stockpiles with additional antiviral drugs including zanamivir (Relenza) based on an evaluation of the performance of these drugs in the scenario that the 2009 H1N1 ‘Swine Flu’ neuraminidase (NA) were to acquire the tamiflu-resistance (His274Tyr) mutation which is currently widespread in seasonal H1N1 strains (Venkataramanan Soundararajan, Kannan Tharakaraman, Rahul Raman, S. Raguram, Zachary Shriver, V. Sasisekharan, Ram Sasisekharan (2009). “Extrapolating from sequence—the 2009 H1N1 ‘swine’ influenza virus”. Nature Biotechnology 27 (6): 510-3). Another example is in the case of the amantadines treatment, which may lead to the rapid production of resistant viruses, and over-use of these drugs has probably contributed to the spread of resistance (Lynch J P, Walsh E E (April 2007). “Influenza: evolving strategies in treatment and prevention”. Semin Respir Crit Care Med 28 (2): 144-58.).
Meanwhile, however, a few strains resistant to neuraminidase inhibitors have emerged and circulated in the absence of much use of the drugs involved, and the frequency with which drug resistant strains appears shows little correlation with the level of use of these drugs (Lackenby A, Thompson C I, Democratis J (December 2008). “The potential impact of neuraminidase inhibitor resistant influenza”. Curr. Opin. Infect. Dis. 21 (6): 626-38.). Laboratory studies have also shown that it is possible for the use of sub-optimal doses of these drugs as a prophylactic measure contributing to the development of drug resistance (Lackenby A, Thompson C I, Democratis J (December 2008). “The potential impact of neuraminidase inhibitor resistant influenza”. Curr. Opin. Infect. Dis. 21 (6): 626-38). Search for a newer class of anti-influenza virus with potency and less side-effects has become a challenge to the bio-medical community.